Antagonist, you're it
This person is an extremely cruel and manipulative individual, who serves as the antithesis of the main protagonist, committing many crimes. This character also had a "sidekick" who was introduced in this series before any of there other appearances.
Who is Joker? (Batman: The Animated Series, not Brave and the Bold lmao)
Who is R2-D2? (Star Wars: The Clone Wars)
This crossover occurred due to one of the protagonist wishing for a better science fair project and seeking the best science laboratory in the universe. This would lead to a series of events, crossing literally two different universes, with even two sequel parts of this crossover of these two shows happening later down the road.
What is Jimmy Timmy Power Hour? (The Fairly OddParents x Jimmy Neutron)
This item is a signature dish to it's home restaurant, being often assembled in the order of: bun, then patty, followed by ketchup, mustard, pickles, onions, lettuce, cheese, tomatoes, and bun. This food also has a coveted "secret recipe" or "formula" attached to it's creation.
What is a Krabby Patty? (Spongebob)
"He could walk through walls, disappear, and fly. He was much more unique than the other guys. It was then that he knew what he had to do."
What is Danny Phantom?
The main perpetrator of the side plot of most episodes, creating many different types of technologies for "evil", yet ultimately never seeing their full intended use due to an easily exploitive self removal feature on these machines. One can even argue this character isn't even really a "villain".
Who is Doofenshmirtz? (Phineas And Ferb)
The companion of this show was first met and obtained at a public fair, once even having a name directly linked to how much it weighed. Though not an impactful character, aside from being the center of the plot in a few episodes, this companion is a fan favorite as well one of the main protagonists.
Who is Waddles? (Gravity Falls)
So, apparently, one of the main characters of one series comes into possession of a sword coveted of a mage who was imprisoned by their half-brother, which leads to a team up from characters of the other show to defeat them, using the latter show's animation as opposed to the medium the first show uses.
What is Ultimate Spider-Man(: Web-Warriors) x Jessie?
This food was created by one of the main characters of this show, being a simple combination of two common items already associated together, being made whilst singing about said item. This little song also for some reason goes really well remixed into the song "Empire State Of Mind" by Jay-Z and Alicia Keys. Yes this is relevant.
What are Bacon Pancakes? (Adventure Time)
"He is a man on a mission. In armor of high tech ammunition. Trapped on the edge of an endless game. His teenage life will never be the same. In a dangerous world he does all he can... "
What is Iron Man: Armored Adventures?
One of the main villains, even among reoccurring weekly antagonists, being considered an archenemy of the heroes, this person utilizing robotic minions and almost superhuman skillset. This character's name is referred to their first name in this show rather than their more well-known alter ego in other depictions of them.
Who is Slade/Deathstroke? (Teen Titans)
Despite being the companion to the characters in this show, one can very comfortable argue this companion is the main character themselves, as they are usually the main if not only force fighting off the oddities and its owners seemly face every other day, despite how remote their home's location is.
Who is Courage? (Courage the Cowardly Dog)
This crossover wasn't an episode or movie, but rather a collection of different series into one type of large multiplayer game in an MMORPG style, even redesigning the characters used in a more "anime" style. The main plot was to stop an evil villain from essentially destroying earth with an army of evil clones.
What is "FusionFall"? (General Cartoon Network MMORPG Game)
This food is assembled as a classic meatball sub, but being made by a master in a deadly martial art, meaning one must wear cut-off jean shorts and a mullet in order to eat it safely, otherwise will mostly experience death shortly after.
What is the Sandwich of Death? (Regular Show)
"Living on the edge. Fighting crime, spinning webs. Swinging from the highest ledge. He can leap above our heads"
What is The Spectacular Spider-Man?
A main antagonist and villain, being the archenemy to the main character due to wishing to take a device and tool the protagonist has. This character has made multiple appearances across this show's runtime and even spinoffs, making you wonder how one can be a conqueror many worlds yet fail this many times.
Who is Vilgax? (Ben 10)
This companion is one that shares a close bond with the main protagonist of this series, over the years they've worked under the same organization. The weapon of choice is that dual wielding hand held laser weaponry due to their marksmanship abilities and human-level intellect, despite their trouble making tendencies.
Who is Bobo Haha? (Generator Rex)
The plot of this crossover involves the characters of show A doing their own thing, a skating competition of all things, whilst the characters of show B arrive to Show A's location as their investigating the local weirdness of Show A. Shenanigans ensue. Also Miranda Cosgrove makes a guest appearance in this episode for some reason.
What is "Lilo & Stitch: The Series" x "American Dragon: Jake Long?"
This type of food was often the main object of desire for the main protagonists of the series, being the core reason they engage with their peers in lucrative gimmicks they devised up. Despite the great efforts the main characters make for this food, the food isn't that expensive, only being about 25 cents per piece, which is a steal considering the common portrayed size of the food.
What are Jawbreakers? (Ed, Edd, n Eddy)
"5 o'clock get a call. To go blading at the skatepark down by the mall. But my mom says I got to prevent hostile aliens from annihilating us all."
What is My Teenage Life as a Robot?
This character is the main "big bad guy" of their respective show, being confronted in the end of the show's story. From most, if not all, interactions and info presented by the show directly show this character to be both a powerful induvial as well power hungry, wishing to conqueror the world with their armies and might. What do you mean that's too generic?
Who is Fire Lord Ozai? (Avatar: The Last Airbender)
The origins of this companion aren't well known until an episode in the late seasons of this show, which reveal this companion obtained new ligaments and physical abilities, in a way upgrading their status as a companion technically. This companion also has 7 names, first, middle and last included, as well being the third in their lineage apparently.
Who is Darwin Watterson? (Amazing World of Gumball)
This crossover starts with characters of show A chasing down an object/thing of interest, encountering the characters of show B, which two of them know each other beforehand from another time. Of course, they team up to defeat the thing causing the object/thing of interest that caused show A characters to be there. This was the season premiere of one of the shows in question interestingly enough.
What is Ben 10: Omiverse x Secret Saturdays?
What are Onigiri/Brock's "Jelly Donuts"? (Pokemon Animated Series)
"I wanna live close to the sun, go pack your bags, 'cause I've already won, everything to prove, nothing in my way. I'll get there one day. 'Cause, I wanna be famous."
What is Total Drama (Island) (Seasons 1-4)